Sunday, May 17, 2009

I'm sorry to have been so long between updates, but the news is relatively benign and we're coming back to the hotel exhausted every day (sometimes twice a day if we're worked really hard). We have covered many of the basics: ile d'citi; tour eiffel, flea markets; seine cruise, etc. Today is for the Louvre and possibly Musee d'Orsay.

But first, I'll try and struggle through our unreliable network and get an update (probably the last) on our current flu outbreak.

The world has taken this outbreak very seriously. WHO has dusted off their brand-spanking-new pandemic phase system and news, especially television news, has given H1N1 the sort of treatment previously limited to wars and major terrorist attacks.

The current data doesn't justify that level of response, but that doesn't mean that we are completely out of the woods yet.

This outbreak appears to be starting to die out. We've been well under exponential growth rates for a week or so and even the current Ground Zero (the US) has been under exponential growth rates for 4 or 5 days. Unless there is another burst of activity, this phase will end by the end of May or so (possibly the middle of June) and we'll all stick our heads back into the ground for a while.

If, however, this flu follows the pattern of the 1918-1920 pandemic, we can expect a resurgence in the fall, which may well be more lethal (the 1918 flu had varying lethality over different phases, but overall was probably the most lethal influenza ever seen). Several processes can contribute to growth in flu's lethality, including progression (as the virus moves from host to host, sometimes it gains potency), transposant changes (the exchange of DNA material from multiple viral strains in one host), and good old fashioned "mutation". The Great Influenza points out that the 1918 flu, by starting out incredibly lethal, almost had to "revert to the mean" and become more benign, but even the more benign strains of the later phases were still twice as lethal as a "typical" flu season.

Two factors combined in the 1918 flu to make the virus more lethal to young adults (20-40) than the typical flu: a previous pandemic (not the 1889, but another, possibly so weak that it had gone unnoticed) had apparently provided older people some measure of immunity to the 1918 flu; and many victims of the 1918 flu were actually killed (or severely weakened) by an immune response rather than the virus itself -- because young adults have stronger immune systems, they were hit harder than children and older patients.

Ultimately, in 1918 the most effective public health response was isolation. A number of locations or organizations enforced strict quarantine and escaped the flu altogether, but army camps, which were notoriously poorly quarantined, proved to be major elements in spreading the disease. Without antiviral drugs or a real understanding of the infectious agent (scientists argued for years over whether bacillus influenzae was the etiological agent of the 1918 flu pandemic, until a "filterable virus" was eventually determined to be the cause), patients were basically on their own against the disease, and the only useful response was a public health one. Because of Wilson's obsession with the war in France, public health took a backseat to military preparedness and morale boosting, and the appropriate public health measures were not taken quickly or strongly.

Mexico's decision to shut down nearly all public events for a week was exactly the right response to create a firewall against the epidemic: flu spreads most easily in crowded conditions, and with a 24-48 hour incubation period, a week was sufficient to slow the spread of the disease. The US response (which was basically to do nothing) has shown to be inferior as the number of cases in the US has risen. Fortunately, we aren't dealing with an extremely lethal strain. This time.

There's not much else to say unless/until the next wave comes around. It wouldn't be surprising to see another outbreak over the summer or into the fall. Whether this particular flu becomes more lethal or less is an open question, and we'll just have to wait and see.